Disclosed herein are various embodiments of an improved method and system for correcting lateral position errors in image rendering systems.
By way of background, digital copiers are well known. Whereas a traditional “analog” copier in effect directly takes a photograph of the image desired to be copied, in a digital copier an original image on an input sheet is recorded as digital data, and the digital data is used to create a print which is a copy of the original image. The original image is typically recorded by an array of photosensors, such as in a charge-coupled-device (CCD), while the printing step is typically carried out by familiar “ink-jet” technology, or by digital “laser printer” rendering in a xerographic apparatus.
Between the recording of the original image and the output of a resulting print, the image data can be processed and manipulated, such as through digital image processing, in any number of ways. Chief among these ways is alteration of the placement of the image relative to a print sheet on which the image is ultimately rendered: the placement of the image further involves consideration of hardware-related factors such as the start-of-scan control in a scanning laser which creates a latent image on a photoreceptor in a xerographic printer, or the precise control of a moving printhead in an ink-jet apparatus. Another aspect of processing image data between recording and printing relates to the magnification of the image.
Ideally, in a basic case, it is desirable that a copy output by a digital copier be as similar to the original image as possible, particularly in the aspects of placement of the image relative to the edge of the print sheet, as well as magnification of the printed image relative to the original.
Now, in any long paper path, due to the increase in the number of paper path nips, there is an increase in paper lateral walk (or displacement). At least one cause of this lateral walk is the misalignment of drive rolls, idler rolls, and mechanical assembly tolerances. The longer paper path causes the paper to walk outside of the input tolerances of the downstream subsystems, thus causing misregistration, marks or jams, depending on the downstream subsystem present.
A registration module may be used to correct for lateral and process position and paper skew. However, the performance of the registration module is based on a trade-off between lateral, process, and skew correction, due to the amount of time that the sheet is in the registration nip. Since the registration module has to work at correcting three aspects—paper skew, paper process position and paper lateral position—there is a limited amount of process and skew correction that can be achieved when correcting large lateral position errors. If the DC lateral shift can be corrected before the sheet arrives at the registration module, then the registration module can correct for larger errors in media process position and media skew.
Thus, the exemplary embodiment disclosed herein relates to an automatic method by which a digital copier can be adjusted to reduce DC lateral position errors prior to registration.